Examples of bi-directional tapered roller bearings are shown in U.S. Pat. Nos. 6,464,401 and 5,735,612, which are incorporated herein by reference. Bi-directional bearings handle axial loads in both axial directions. Such bearings include a cone defining a tapered inner raceway, a cup defining a tapered outer raceway and a plurality of tapered rollers between the inner and outer raceways. The bearing assembly includes at least a thrust rib on the cup adjacent the large diameter end of the roller and a second rib on the cone adjacent the small diameter end of the roller. The two ribs have associated rib faces, and the rollers are positioned between the two rib faces. In contrast, a uni-directional tapered roller bearing will have only a single thrust rib.
Bi-directional tapered roller assemblies are susceptible to abrasive and adhesive wear at the sliding contacts between the rolling elements and the cup/cone rib faces in the presence of debris or in low lubrication (e.g., oil-out) conditions. Experiments have shown that both internally generated and external debris are especially harmful at the rib-roller end contacts because they can become trapped within the multi-rib bearing and cannot easily flow away from the rib/roller end contacts. Similarly, the presence of extra rib-roller end sliding contacts relative to single rib tapered roller bearing designs can make bi-directional tapered roller bearings more susceptible to rib-roller end scuffing or scoring damage in oil-out condition.